Vehicle outer-door access handles often utilize electro-mechanical switches or capacitive sensors to determine user interaction with the handle surface in order to initiate unlock/lock commands, input access codes via a keypad in the handle, etc.
While electro-mechanical switches are advantageous because of low cost and low drain on the vehicle's power system, they do have several drawbacks, including the following: First, electro-mechanical switches may include moveable buttons and actuators for a user to interact with. Yet, current handle design aesthetics favor “clean” surfaces with minimal gaps or disruptions. Second, only limited information about a user's interaction with the electro-mechanical switch can be obtained. Typically, for instance, only open and closed states of the switch can be determined. Third, the typical actuation forces required of electro-mechanical switches are around 8 Newtons, with travel distances typically being relatively great at at least 1.0 mm. Lower actuation forces and/or travel distances are difficult to design with electro-mechanical switches. Fourth, electro-mechanical switches can be difficult to seal with respect to the environment outside of the vehicle. Failed sealing can result in contamination or oxidation of the switch contacts, which in turn may result in switch failure. Fifth, electro-mechanical switches require tuning of the mechanical movement to achieve a desired “feel” for the user and to eliminate “button wobble.” Sixth, the life of the mechanism is limited by the moving elements thereof. Seventh, 10 mS or more of contact “de-bounce” time is required to acquire a reliable state or output in the switch.
Capacitive sensors, by comparison, measure the change in a capacitive field generated on the touch surface. But while these sensors have their own advantages, they also have drawbacks, including the following: First, capacitive sensors have difficulty sensing covered (e.g., gloved) hands. Second, capacitive sensors have trouble discriminating between intended and inadvertent contacts, sometimes yielding an undesired effect (such as an unintended vehicle unlocking/locking). Third, capacitive sensors can be erroneously activated by water (such as from rain, car washes, etc.). Fourth, any conductive metal placed on the sensing surface can be interpreted as a touch. Fifth, touches on individual areas of the sensor cannot be distinguished from each other; the sensor can only determine whether or not contact has been made. Sixth, electromagnetic interference can be erroneously interpreted as a touch. Seventh, the long response time (>200 mS) often programmed into capacitive sensor systems to discriminate between a true touch and a false signal can be an annoyance to users desiring a more rapid response time.